Polyester resins as represented by a polyethylene terephthalate have excellent properties such as moldability, transparency, mechanical strength and resistance against chemicals, as well as excellent gas barrier property such as against oxygen and can, hence, be used as packaging materials such as films, sheets and bottles in a variety of fields.
In order to enhance the gas barrier property of the above packaging material, further, there has been proposed a packaging material having a functional resin layer comprising a gas barrier material such as a saponified product of an ethylene/vinyl acetate copolymer or a polyamide as an intermediate layer between the inner layer and the outer layer. The above packaging material, however, is accompanied by a problem of interlayer peeling due to low adhesion strength between a functional resin constituting an intermediate layer and a resin (e.g., a polyester resin) constituting the inner and outer layers.
In the multi-layer structure for packaging having the functional resin layer as the intermediate layer between the inner layer and the outer layer, therefore, it is a generally accepted practice to provide adhesive layers among the functional resin layer and the inner and outer layers to increase the adhering strength and to suppress the interlayer peeling.
There has been known, for example, a laminate having graft-modified ethylene/α-olefin random copolymer layers (adhesive layers) provided among the polyester resin layers (inner and outer layers) and a layer of a saponified product of an olefin/vinyl acetate copolymer (functional resin layer)(Japanese Unexamined Patent Publication (Kokai) No. 62-158043).
There has further been proposed a multi-layer container having a mixed resin layer obtained by mixing a gas barrier resin into a polyester resin, the amounts of the polyester resin particles and of the gas barrier resin particles of not larger than 10 μm being not larger than 10%. According to the above multi-layer container, the adhesion among the layers can be improved without decreasing the transparency (Japanese Examined Patent Publication (Kokoku) No. 8-25220).